(1) Field of the Invention
The present invention relates to a grained artificial leather having good color fastness and to a process for dyeing ultrafine polyamide fibers into deep, bright colors, keeping good color fastness to dry cleaning in charged system.
(2) Description of Prior Art
The grain layers of conventional artificial leathers are made by providing porous or/and non-porous layers of such resins as polyurethane on the porous sheets made of elastic polymers and fiber base such as nonwoven fabric, knitted and woven fabric. However, such resins do not show good dyeability and color fastness, especially to dry cleaning.
Therefore, dope dyeing has been applied to the resins of the grained surface. However, dope dyeing is not suitable for manufacturing artificial leathers of many colors, each quantity of which is not large. Further, the appearance of such artificial leathers is monotonous and opaque due to lack of transparancy and luster.
On the other hand, Japanese Patent Publication No. 28041/1973 teaches that some kinds of polyurethane whose soft segment is polyethyleneglycol (PEG-type PU) can be dyed with metal complex dyes. However, the artificial leathers comprising PEG-type PU and fiber base of ultra-fine fibers have no great practical value because they have not good color fastness as a whole, owing to insufficient color fastness of the ultra-fine fibers. Further, when the fiber base is impregnated or coated with porous resins, the porous resins, whose color fastness to dry cleaning is poor, spoil the appearance of the artificial leathers seriously, not only at the back surface but also the grained surface. The faded porous polyurethane affects the appearance even through the dyed grained surface.
On the other hand, a number of proposals have been made as to leather-like fabrics made of ultrafine fibers, such as suede-like, nubuk-like, woven or knitted fabrics, as well as grained artificial leathers. And, now, extra ultrafine fiber around or less than 0.01 denier is attracting our interests to obtain softer hand or more dense appearance.
However, as fibers become more fine, dyeing deeply and brightly becomes more difficult because of increased surface reflection of the extra fine fibers.
For example, though polyamide fibers such as nylon-6 and nylon-66 have such advantages over polyester fibers as softess, high wear resistance and brightness of color, the use of polyamide ultrafine fibers for clothing has been delayed so far because dyes are very liable to come off in washing and dry cleaning. The reasons of the insufficient color fastness are not known in detail.
Japanese Patent Publication No. 8128/1981 mentions attempts to improve color fastness by increasing molecular orientation of ultrafine nylon fibers. However their color fastness are insufficient to the dry cleaning in which charge soap is used. The extra-ultrafine fibers around or less than 0.01 denier always show complete fading of color even if they are dyed with the dyes said to give the highest color fastness to fibers of ordinary thickness.
Though thren-type vat dyes (vat dyes derived from anthraquinone) can be also applied to composite sheets of ultrafine polyamide fiber and polyurethane (Laid-Open Japanese Patent Application Publication No. 1365/1980), they can neither give any heavy shade nor show good resistance to synthetic solvent for dry cleaning. Further, they cause photo-tendering for some hues; also the strong base used in dyeing leads to deterioration of polyurethane.